JPH04229994A - X-rays film exposure time automatic de- cision method and embodied device - Google Patents

Abstract

PURPOSE: To automatically determine optimum exposure time by measuring and estimating the amount of X-ray radiation passing through an examined material body. CONSTITUTION: An examined material body 13 is irradiated with an X-ray beam 14 radiated from an X-ray source 11, and a detecting cell 12 intercepts X-rays transmitted through the examined material body 13 and the image receiver 17. Subsequently, an output signal L of the detecting cell 12 is input to an integrating circuit 16, and the amount of X-rays transmitted through the examined material body 13 during exposure is estimated to input an output M to a calculator 18. Furthermore, a microprocessor 19 computes the exact amount of radiation from a voltage Vm and current I of an electric power unit 15 of the X-ray source 11, and from a time S, and then calculates optimum exposure time to control the electric power unit 15.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention comprises an X-ray film,
It relates to X-ray equipment used for inspecting objects,
In particular, in such an X-ray device, the "illumination" or "
It relates to a method that can predict the amount of exposure (i.e., the product of the amount of light received and the exposure time) and stop exposure when the degree of darkening or optical density of the film reaches a predetermined level. .

0002

2. Description of the Related Art An X-ray apparatus includes an X-ray tube and a radiation receiver, between which an object to be examined, for example a part of a patient's body, is placed. An image receiver, for example a film/sensitizer combination, provides an image of the object to be inspected after development of the film at the appropriate exposure time. In order to use the image of the object to be inspected as effectively as possible, each dot that makes up the image must have sufficient contrast with respect to the other dots, i.e. the degree of blackening of the X-ray film must be , the opacity of the object to be inspected from which an X-ray photograph was taken may vary, but the opacity must be optimal for each X-ray image. The degree of blackening of a film is a function of the amount of radiant energy incident on the film/sensitizer pair, i.e. the intensity of the radiation to which the X-ray film is exposed, i.e. the product of the "film" dose rate and the time during which the film is exposed to this radiation. Involved. Therefore, in order to obtain a constant degree of film blackening with each X-ray exposure, during the inspection, an X-ray
It is known to measure the energy incident on a film by means of a detection cell which, in response to radiation, provides a current proportional to the "film" dose rate. This current is integrated from the beginning of the exposure in an integrator circuit which outputs a value that increases during the exposure. During the exposure time, this increasing value is compared to a fixed reference value previously set as a function of the film properties. The end of the exposure time is determined by the moment when the comparison shows that the value representing the energy incident on the film is equal to the reference value. When the X-ray film is directly exposed to X-ray irradiation and the change in exposure time for each inspection is sufficiently small, if the product of exposure time S and dose rate F is constant, that is, the value of the integral result is constant. , a constant degree of film darkening is obtained with each exposure, independent of its exposure time S. This is true only if the properties of the film obey the reciprocity law that the optical density of the film is proportional to the product F×S, and the response of the film is independent of the incident x-ray beam. When the change in exposure time is large, this reciprocity law no longer holds. Also, when an X-ray film is combined with an intensifying plate, the degree of blackening of the film is determined by the spectral quality. That is, the response of the sensitizer plate is
This is because it is determined by the spectral energy distribution of the received radiation, that is, the spectral hardness and
This is because it means being sensitive to changes in the voltage of the tube. Furthermore, since the radiation energy then causes the detection cell to be visible on the film, there are applications (eg mammography) where placing the detection cell in front of the film is costly. In this case, the detection cell is placed after the image receiver, but this placement causes another problem since the signal perceived by the detection cell does not contribute to the degree of film darkening. As a result, measurements made by the detection cell typically do not indicate the incident illumination on the X-ray film. The deviation from the reciprocity law varies depending on the film type and indicates the relative change in illumination required to obtain a constant optical density when the X-ray exposure spectrum is constant and the exposure time S is varied. This means that to obtain the same optical density of the film,
For example, 1 when exposure time S=0.1 seconds and 1 when S=1 second.
3, S=4 seconds and 2. This deviation from the reciprocity law is due to a phenomenon known as the Schwarzschild effect. This effect is especially true for Pierre GLAFK.
IDS)'s book ``Chemistry and Physics of Photography'' (CHIMI
E ET PHYSIQUE PHOTOGRAPH
QUES) 4th edition, pp. 234-238 (Publication Foto-Cinema Paul Montel)
PUBLICATIONS PHOTO-CINEMA
Paul MONTEL)).

Various methods have been proposed to account for this deviation from the reciprocity law. One such method is described in French Patent No. 2,584,504. This patent proposes to compare the integral value of the signal output by the detection cell with a reference value that varies during the exposure time according to a certain relationship. More precisely, starting from the beginning of each exposure time, a complementary value is added to the difference between the value of the integral signal and the reference value. This complementary value increases as a function of time according to a predetermined relationship, for example an exponential relationship. This predetermined relation, whether exponential or not, takes into account deviations from the reciprocity law, but it is only incomplete. In particular, it does not take into account the changes in light intensity effectively experienced by the film. Furthermore, this correction does not take into account the effects of other phenomena such as hardening of the X-ray irradiation due to the thickness of the object through which the X-rays pass and changes in the spectrum due to the voltage between the X-rays. Also in this method, the detection cell is placed in front of the image receiver.

0004

SUMMARY OF THE INVENTION It is therefore an object of the present invention to take into account the various effects acting during the exposure time, in particular changes in the current of the X-ray tube, hardening of the spectrum due to the thickness of the passing object, Considering the change in the spectrum due to the voltage of the tube and the absorption response of the intensifying plate when it is present,
The objective is to provide a method for automatically determining the moment to stop exposure.

[0005]

SUMMARY OF THE INVENTION The present invention provides an
for X-rays passing through the object to be examined so as to form an image of the object, constituted by a ray tube, at least one intensifying plate and a film sensitive to the light emitted by this intensifying plate; an X-ray receiver and a cell for detecting the X-rays that have passed through the object to be examined, which is arranged behind this X-ray receiver and is capable of converting the physical variables characterizing the X-ray beam into a measurement signal L. , an integrating circuit that integrates the measurement signal L during the exposure time S and outputs the signal M, and the product I×S (or mA.
s) a device for calculating the radiation dose D given as the ratio of M to A method for automatically determining the exposure time of an x-ray film in an x-ray apparatus, comprising the steps of: (a) using a receiver without one or more intensifying plates; , a first calibration of the X-ray imaging device is carried out by an object of thickness Ep, with the following function; Dse=f' (Vm, Ep
) (
4) and the following inverse function; Ep = g' (Vm, Dse)
(5) and (b) perform a second calibration of the X-ray imaging device with an object of thickness Ep using a receiver with an intensifying plate to obtain the following function; Dc = f'' (Vm, Ep)
(6) The following inverse function; Ep = g'' (Vm, Dc)
(7) and the following function; Df = f' (Vm, Ep) -
Determine f''(Vm, Ep) (8) and (c)
performing a third calibration that determines the reference illumination Lref that the film must undergo under certain reference conditions to achieve a degree of blackening (or optical density) selected as a reference value by the user; The present invention relates to a method characterized by comprising the following steps.

[0006]

[Operation] When performing these calibrations, the following steps are performed: (e1) Determination of the position of the object to be X-rayed; (e2)
) Trigger of initiation of exposure by user, (e3)
After the start of exposure, measurement of the radiation dose Dc1 at time t', (e4) calculation of the equivalent thickness E1 according to equation (7), (e5) radiation dose in a film of thickness E1 according to equation (8) Calculation of Df1, (e6) formula
Lf=Lam+Df1×δmA. s
Calculation of the illumination Lf received by the film according to (9), (e7) formula
Lra=Lref-Lf
(10) Calculation of the illumination Lra necessary to obtain the degree of blackening (or optical density) determined by (e8) Formula mAs
r=Lra/Df1
To obtain the blackening (or optical density) determined by (11), an approximate mA. Calculation of mAsr giving s, (e9) From the starting point of work (e3), mA. The measurement of mAsmes giving s, (
e10) mA. measured in (e9). When the measured value mAsmes of s is equal to or greater than mAsr, the exposure is stopped and the mA. When s is smaller than mAsr, it is possible to carry out an X-ray examination of the object, which consists of returning to step (e3). The above step (e8) is the period t of the above steps e4 to e8.
During c, the formula; mAsc = I×tc

(13) defined by mA. mA giving s
Calculate sc and use the formula; mAsra=mAsr − mAsc

(12), the mA. The actual value of s mAsra can be determined.

[0007] In the first modification, the above step (e10)
further has the formula; trc=mAsra/I
(
14) Calculate the remaining exposure time trc shown by t
It includes stopping the exposure when rc becomes less than a value t0 corresponding to the interval between two successive steps (e3). In the second modification, from the above step (e3) to (e1
0), the following operations; steps (e4) to (e8),
mA. CEtarget=mAsra
×Dc
(16), the mA to be given is converted into a signal in units of 12 cells. The prediction task (T.E.) that predicts s decrements the target value CEtarget according to the signal received by the cell, and the decremented value becomes the value Val0 (Val0 is, for example, 0).
When this happens, it is replaced by a interrupting task (T.C.) consisting of terminating the exposure. The prediction task (T.E.) consists of:
Moments t1, t2, separated from each other for a period longer than the calculation time tc,
... is periodically updated with tn. In another variant, step (e10) is replaced by a step of calculating the remaining exposure time trc and terminating the exposure in open loop. In yet another variation, Lf = Lam + Df1 x δmA.
s/CNRD (film dose rate) (9') and mAsra=(Lra/Df1)×CNRD(
film dose rate) (11') (where, in these formulas, CNRD (film dose rate) is a non-reciprocal coefficient indexed as a function of the film dose rate at the receiver, and the film dose rate is: Df1×I

(1
7) Modify steps (e6) and (e8) to take into account the non-reciprocal effects expressed as . The above coefficient CNRD (film dose rate) is determined in the following steps: Measure the non-reciprocity coefficient CNRT(ti) of the film/sensitizer pair as a function of the exposure time (ti) and calculate the film dose rate (di) for each exposure. The time (ti) is measured and the formula; CNRD(d)=A'0+A'1log(
1/d)+A'2[log(1/d)]2 (20) Calculate the standardization function of the coefficient CNRD(di), thereby calculating the coefficient corresponding to a given film dose rate. obtained by doing. For example, the film dose rate is calculated using the formula di = [Lref × CNRT(ti)]/
ti (22).

The reference illumination is determined by a calibration method that includes the following steps (or operations): reference optical density DOref0, standard thickness E0, supply voltage V0,
The image is taken under predetermined X-ray imaging conditions of the exposure time t0 and the value of the product I0 × t0, and the radiation dose D0 is measured using the formula Ep0=g'' (V0, D0)
Calculate the equivalent thickness Ep0 by (7) and use the formula Df0=f'(V0,E0)-f''(
V0, E0) Calculate the radiation dose Df0 on the film by (8) and use the formula Lfilm=Df
0×I0×t0
(23) calculate the brightness Lfilm on the film, calculate the illumination stage Echref corresponding to the reference optical density DOref0 by the sensitivity curve, measure the optical density DOm of the obtained photograph, and calculate the illumination stage Echm by the sensitivity curve. Calculate, formula; L
ref =Lfilm×exp [log10[(Ec
href −Echm )/K]] (25)
(However, K=2/log10(2)

Calculate the reference illumination by (26) ). The non-reciprocity coefficient CNRD (
d) the following steps; measuring the non-reciprocity coefficient CNRT(ti) of the film/sensitizer pair as a function of the exposure time (ti) and measuring the film dose rate (di) for each exposure time (ti); and the formula; CNRD(d)=A'0+A'1log(
1/d)+A'2[log(1/d)]2 (20) Calculate the standardization function of the coefficient CNRD(di), thereby calculating the coefficient corresponding to a given film dose rate. obtained by doing. The non-reciprocity coefficient CNRT(ti), which is a function of the exposure time (ti), can be determined in different ways, for example by: (a1) changing the X-ray tube heating current to obtain different values of this current; (a2) Read the value M(ti) output by the integrating circuit for each different exposure time, obtain the optical density D01 of the film, and (a3) calculate the ratio
M(ti)/M(tref)
(29)
, so that if ti = tref , then
The coefficient C with M(tref) is the value M(ti)
It is obtained by calculating NRT(ti). The coefficient CNRT(ti) is a function of the following: CNRT(t)=A0+A1 log t+
It is standardized by A2[log t]2 (18).

When the image receiver of the X-ray imaging device is of film type and the detection cell is placed in front or behind the image receiver, the above operations a, b, c and steps e1 to e1 are performed.
0 is reduced to the following steps. (a') Using film as an image receiver, calibrate the above X-ray device to form the following analytical model; D'f = f''' (
Vm, Ep) (
30) Determine (c') the reference illumination L'ref that the film should undergo by calibration under certain reference conditions, using the film as an image receiver.
(e'1) determine the position of the object to be radiographed; (e'2) the user Trigger the start of exposure, (e'3) measure the radiation dose D'f1 at time t' after the start of exposure, (e'
6) Formula; L'f = Lam + D'f1 x δmA
．． Calculation of the illumination L'f experienced by the film by s (film dose rate) (9''), (e'
7) Formula; L'ra=Lcvn -L'f

The illumination L'ra required to obtain the selected degree of blackening (or optical density) by (10'')
Calculation, (e'8) Formula; mAs'
To obtain the selected degree of blackening (or optical density), the approximate mA. mAs'r giving s
The calculation of a and the following other steps e9 and e10 are unchanged. Other objects, features and advantages of the invention will become apparent from the following description of the method according to the invention with reference to the accompanying drawings and an example of an X-ray imaging device used to carry out the method. .

0010

[Embodiment] An X-ray imaging apparatus to which the method according to the present invention for automatically determining the exposure time of an object to be inspected 13 to be X-rayed is capable of applying an X-ray beam irradiating the object to be inspected 13. An X-ray source 11, such as an X-ray tube, is positioned to receive the X-rays passing through the object, and after an appropriate exposure time S and development of the film, a film/film is positioned to receive the X-rays passing through the object. An image receiver 17 such as a sensitizing plate is provided. In order to implement the method of the invention, the device further comprises a detection cell 12 . This detection device is arranged behind the image receiver 17 in the case of an X-ray film with an intensifying plate. In the case of films without intensifiers, this detection cell can be located in front of the image receiver. By means of this detection cell 12, a physically variable characteristic value of the X-ray radiation that has passed through the object and the image receiver, such as KERMA or an energy flow rate, can be converted into a measurement signal L, for example of electrical type. The signal L output by the detection cell 12 is input to an integration circuit 16 which performs integration during the exposure time S. The signal M generated from the integration is the exposure time S
This is a measurement of the X-ray radiation that has passed through the object 13 to be inspected. The X-ray source 11 is connected to a power supply 15 which supplies the X-ray tube with a variable high voltage Vm and which comprises a device for measuring the anode current I of this tube. In order to change the exposure time S, the supply device 15 and the X-ray tube start emitting X-rays at a precise moment and, according to the method of the invention, the signals M and I, S and ceasing its emission after a variable time S determined as a function of the value of Vm and, more precisely, the ratio M/(I×S), called the radiation dose D and calculated by the calculation device 18; Have the means. The value of the radiation dose D is processed by the computer or microprocessor 19 according to the method of the invention to output an end-of-exposure signal.

The first task of the method consists in performing a calibration of the X-ray imaging device of FIG. 1 to derive a function of the measurement of the illumination experienced by the X-ray film. This calibration and measurement function is described in the METHOD FO ``Measurement and Calibration of Illumination Exposed to X-ray Films'' filed on the same day.
R THE ESTIMATION AND CALI
BRATION OF THE LUMINATION
RECEIVED BY A RADIOGRAPH
IC FILM). To understand the following part of the explanation, the method of measuring the illumination undergone by an and a calibration used to establish a relationship between the film dose rate function and the illumination that the film undergoes under certain reference conditions, resulting in a predetermined degree of darkening of the film. This latter calibration will be discussed in detail below. The calibration with which the film dose rate can be determined is described in the ``METHOD FOR THE CALIB
RATION OF A RADIOLOGICALS
YSTEM AND FOR THE MEASURE
MENT OF THE EQUIVALENT TH
No. 07/535,520, filed June 8, 1990, entitled "ICKNESS OF AN OBJECT". The method consists of measuring the radiation dose D of the detection cell for each standard at the selected supply voltage Vm. More precisely, with the first thickness standard E1, the radiation dose D1m is measured for each value Vm constituting a predetermined set. Graphing these values D1m as a function of voltage Vm gives point 21' in FIG. If the measurement of the radiation dose D is carried out for another thickness standard E2, a value D2m is obtained which corresponds to point 22' in FIG. Thus, when the operations are performed successively, the radiation doses D3m, D4m and D5m and the thicknesses E3 and E4 are respectively
A series of points 23', 24' and 25' corresponding to E5 and E5 are obtained.

It should be noted that in FIG. 2, the radiation dose DPm is shown as a logarithmic y-axis value and the supply voltage as an x-axis value from 20 to 44 kV. These series of points 21'-25' are used to determine the parameters of an analytical model that determines the behavior of the radiation dose D as a function of the parameters Vm and Ep for a given configuration of the radiographic device. This analytical model has the following formula; D=f(Vm, Ep)
It is shown by (1). The parameters of the analytical model are adjusted by standard measurement tools such as the minimum mean square error method. Curves 21 to 25 are calculated using the following formula; D=f(Vm, Ep)=exp[f1(V
m)+Ep×f2(Vm)] (2) However, in the above formula, f1 (Vm) and f2 (Vm
) is a second degree polynomial and is shown as follows. f1(Vm) =A0 +A1Vm +A2Vm2 f
2(Vm)=B0 +B1Vm +B2Vm2 The value of the radiation dose D provided by the analytical model is illustrated. If D and Vm are known, then by the inverse function of the function given by Equation 2, Ep=g(Vm,D)=[Ln(D)−f1(Vm
)]/f2(Vm) Ep can be calculated by (3). However, the radiation dose D is the voltage Vm
It is well known that f2 (Vm) cannot be nullified with the current value of Vm because it always changes with the thickness Ep. In other words, the values (Ep, Vm
) corresponds to the measurement of the radiation dose D, allowing Ep to be determined as a function of Vm and D. During an X-ray examination, the measurement of the radiation dose D carried out at a given supply voltage Vm makes it possible to determine the equivalent thickness in the units used for Ep. This calibration is carried out twice for the image receiver 17 in different X-ray imaging device configurations. The first of these calibration operations is performed using an image receiver 17 without an intensifier. The function f' is determined according to equation 1, and the following equation; Dse=
f'(Vm, Ep) (4)
The value Dse of the reference detection cell 12 such as and the following formula; E
p = g' (Vm, Dse)
Obtain the value of the inverse function of (5). A second operation of the method of the invention comprises a second operation using an image receiver 17 comprising an intensifying plate.
, and then a series of radiation dose values Dc is obtained and, as above, the following equation; Dc =
f''(Vm, Ep) (6
) as the function f'' and the following equation; Ep = g'' (
The inverse function of Vm, Dc ) (7) is determined.

From the two calibration operations described above, a function Df is deduced that describes the radiation dose on the film. The function Df is given by the following formula; Df = Dse-Dc
That is, Df = f' (Vm, Ep) - f'' (V
m, Ep) (8) This function Df is the function of the X-ray radiation spectrum due to the additional filtering between the intensifier and the detection cell 12, e.g. coming from the output side of the cartridge containing the film/intensifier. Not considering changes. To take that into account, Ep in equation 8 should be changed to (Ep −sup.filter)
(where sup.filter is equivalent to the thickness of the X-rayed object corresponding to this filtering effect). This equivalent thickness can be determined, for example, by placing an object equivalent to this filtering effect in the beam 14 and using a calibrated function to determine the equivalent thickness g' or g'' depending on the machine configuration. obtained by Df×I
Since the product of ×t is proportional to the energy absorbed by the intensifying plate at the anode current I during period t, the quantity Df that is referred to as the film dose rate ×I is the dose of incident photons on the film. is proportional to the rate and is expressed in units of measurement of the signal of the detection cell 12. This law of proportionality is more efficiently confirmed since the number of photons emitted by the intensifying plate is itself proportional to the energy absorbed. If the number of photons emitted by the intensifying plate satisfies another relation as a function of the absorbed energy, then this other relation can be written as D
It is necessary to fit f ×I and obtain the film dose rate.

The final calibration consists of coupling the electrical function described above to the darkening value of the film, ie the optical density to be obtained at the end of the exposure. This value is selected by the user as a function of the film/sensitizer set, the type of diagnosis, the part of the patient's body to be examined and the user's conventional method of examining radiographs. This selection makes it possible to determine the reference illumination Lref, ie the illumination that the film must undergo in order to reach a certain degree of darkening in this way under certain reference conditions. The method used to determine Lref is described below. These calibration operations are not carried out every time an object or patient is examined for X-ray exposure, but each time the changes in the characteristics of the X-ray imaging device during that time,
In particular, consider changes such as aging of the X-ray tube. The results of these operations are recorded in the memory of microprocessor 19 as functions shown by equations 4-8. This is Dc
This shows that if , the microprocessor 19 can calculate Ep and therefore Df.

During an X-ray examination of a patient, the method according to the invention further consists of performing the following main steps (or operations): (e1) positioning of the object to be X-rayed; (e2)
Trigger of the start of exposure by the user, (e3) measurement of the radiation dose DC at time t' after the start of the exposure, (
e4) Calculation of equivalent thickness from radiation dose DC K measurement, (e5) Calculation of radiation dose Df1 in film,
(e6) Calculate the illumination that the film has undergone from the start of exposure; (e7) Calculate the illumination required to obtain the selected degree of darkening (or optical density); (e8) Obtain the selected degree of darkening. The approximate mA. emitted by the X-ray tube for. Calculation of s, (e9) m emitted from the beginning of the exposure or from the above measurements, as the case may be.
A. Measurement of s (referred to as mAsmes), (e10)
When mAsmes is equal to or greater than the calculated mAsr, stop the exposure, and when it is smaller, return to step (e3). It should be noted that the term "illumination" is defined as the amount of light received (dose), eg, the product of the illuminance EC of the photosensitive surface and the exposure time. Step e3 includes the calculation device 18 at a time t' after the start of the exposure.
It consists of measuring the integral value D output by
However, it is known that the integrator circuit 16 is optionally set to zero at the beginning of the exposure or after the last measurement. The integration time t' corresponds to the time elapsed since the start of the exposure or the time elapsed since the last measurement, as the case may be. Step e4 is carried out by the microprocessor 19 from the first calibration of the X-ray imaging device, as described above. This step is governed by Equation 7, and then the equivalent thickness value E1
is obtained. In the second and subsequent iterations of the method, it is not necessary to carry out step e4, as the measurement of the equivalent thickness was made sufficiently accurate during the first iteration. stage e5
is the thickness E1 using the function defined by Equation 8
consists of calculating the radiation dose of the film Df1 corresponding to . Thereby, in particular, the influence of the intensifying plate of the image receiver can be taken into account. This operation was briefly described above. Step e6 is based on the following equation: Lf = Lam + Df1 x δmA. s
(9) (where Lam is the illumination that the film has undergone before stage e3, δmA.
s is the mA.s emitted by the tube during time t'. s, defined by the product of the tube current I and the integration time S) to calculate the illumination Lf experienced by the film from the beginning of the exposure. Step e7 is
It consists of calculating the remaining illumination Lra necessary to obtain a predetermined degree of blackening. This is the following equation 10
Calculated by; Lra=Lref −Lf
(10) Step e8 includes the remaining mA. s, which is calculated according to the following equation 11: mAsr=Lra/Df1
(11) Next, the mA released during the calculation
．． The number mAsc of s can be deduced. Therefore, the actual remaining mA to be acquired. s is defined by the following formula; mAsra=mAsr-mAsc
(12) However, mAsc=I×tC
(13) (where tC is the time taken for the calculation) Step e10 consists of making the following selections: That is, to recalculate the value of the remaining mAs to be emitted, or to stop or continue the exposure again still depending on the exposure time, or to recalculate the measurement value at the end of the exposure time.

The criteria for ending exposure is determined as follows. Value of the following formula: Dif(mA.s) = mAsra-mAsmes
When (15) is 0 or smaller than a certain value Val0, the microprocessor 19 acts on the power supply 15 to stop the X-ray irradiation. If not, return to step e3. The following relational expression; t
rc=mAsra/I
A supplementary test can be performed for the value of the remaining exposure time trc defined by (14). This supplementary test consists in not changing the measured value mAsra when trc is less than t0. At that time, exposure termination is the exposure termination operation, i.e., the emitted mA. When the number s is decremented and this number becomes less than zero, the process ends in an open loop while only stopping the exposure. Possible values for t0 are approximately equal to the time interval between the two measurements corresponding to step e3. In this case, therefore, operation e10 comprises two tests: - a first test on mAsra to determine whether the exposure should be stopped; - a new measurement of the remaining mAs to be emitted or the value Second test on trc to determine whether mAsra is fixed until the end of the exposure. In this case, an exposure termination test is performed periodically for mAsra. Additionally, the operation of measuring the remaining elapsed time and the exposure stop device can be performed separately to further improve the accuracy of the exposed object. Therefore, this method separates as follows. i.e. the remaining mA to be released before the end of the exposure
．． Task T. to measure s. E. and task T. to stop the exposure. C. It is. Remaining mA to release
．． Task T. to measure s. E. is the operation e3~e
8, in addition to mA.8. s as below, CEtarget=mAsra×Dc
(16) Add a device e'9 that converts the signal within the device of the detection cell 12. This prediction task T.
E. are measurement times separated by periods at least equal to the calculation time tc during the exposure, t1, t2...
・Updated periodically with tn. Prediction task T. E. At the end point, the target value CEtarget is updated. This update is done at the measurement time and at the beginning of operation e3 and the value CEtarge
t is operation T. E. The signal received by the detection cell 12 between the time it was updated at the end of the process must be taken into account. Task T. to stop exposure. C. consists of decrementing a predetermined value (or target value) as a function of the signal received by the detection cell 12. This task returns the value CEtarget
Exposure is stopped as soon as becomes below Val0, which is zero, for example. Therefore, task T. C. can be summarized in the following steps (or operations): (f1) measuring the integral signal Mm by the detection cell 12 after a certain time ttc, (f2) decrementing this value from the target value (CEtarget-Mm)
, (f3) (CEtarget-Mm) is Va
Stop exposure when lower than l0, otherwise (f
Return to 1).

The above method works correctly as long as the image receiver 17 and the detection cell 12 do not deviate from the reciprocity law. If this is not the case, the correction factors must be determined by specific measurements and calculations, supplementing operations e6 and e8 to take this into account. This correction factor is introduced into Equations 9 and 11, where the illumination and film radiation doses act. Therefore, equations 9 and 11 become: Lf=Lam+Df1×δmA. s/CNR
D (film dose rate) (9') mAs
ra=(Lra/Df1)×CNRD (film dose rate) (11') However, film dose rate=
Df1×I (17) where CNRD is a non-reciprocal function shown as a function of the photon dose rate on the film. The function CNRD is based on the ``Method for measuring functions showing non-reciprocal action of X-ray film'' filed on the same day.
TERMINATION OF THE FUNCTI
ON REPRESENTING THEEFFECT
OF NON-RECIPROCITY OF A
RADIOGRAPHIC FILM)" by the calibration method described in the patent application entitled "RADIOGRAPHIC FILM". To understand the following discussion, it may be noted that this calibration method consists first of measuring the non-reciprocity coefficient of the film as a function of the exposure time ti. This function is CNR
It is written as T(ti). Although this function CNRT is determined experimentally, it can be expressed as an analytical function. More precisely, this method uses different irradiation intensities IRi
, a constant optical density DOrefo of the film, e.g. D
It consists of measuring the value ti of the exposure time required to obtain Orefo=1 and reading the value output by the integrating circuit 16 at each exposure time ti, ie the value called M(ti). These values are compared with a reference value M (tref), which is a value corresponding to 1/2 the exposure time, and the ratio M (ti
)/M(tref) (2
9) Calculate. It is this ratio that determines the in-time non-reciprocity coefficient CNRT(ti) at the exposure time ti.

Another method for determining the coefficients CNRT(ti) is described below. These coefficients CNRT(ti)
are intermittent with each other as a function of exposure time according to the curve of FIG. 3, for example, for optical density DOrefo=1 and reference exposure time tref=1 second. This curve shows that the illumination required to obtain the desired optical density increases with exposure time. Therefore, in this example, the ratio of the energies of the two exposure times of 50 ms and 6.5 s is approximately 1.6. The curve in Figure 3 is normalized by a function with the following equation 18: CNRT(t) = Ao + A1 log t+
A2[log t]2 (18) (However, in the above equation, those parameters Ao, A1 and A2 are measured from the measurement point by the minimum error square measurement method.) In principle, equations 9' and 11' The Schwarzchild effect taken into account is the function C
Standardized by NRT. The advantage of using the film dose rate function CNRD is that changes in the anode current can be taken into account. Therefore, an autoexposure device using the function CNRT according to equations 9' and 11' is
For example, there is an advantage that the tube operates with reduced load. From the time display coefficient CNRT(t) to the rate display coefficient CNRD(d
), it is necessary to take into account the fact that the coefficient CNRT(t) is determined by measuring with varying exposure times under conditions where the value of the photon dose rate on the film is not necessarily known. . When the film dose rate di is measured for each exposure time ti, the value of the coefficient CNRD(di) for di is the corresponding exposure time ti
is equal to the value of the coefficient CNRT(ti) at
(19) holds true. These CNRs
The values of D(di) are related to each other by a curve (FIG. 4) as a function of the reciprocal of the dose rate 1/d. This curve is calculated by the following equation 20: CNRD(d)=A'0+A'
1 log (1/d) + A'2 [log 1/d] 2
(20) is standardized by a function with . value di
Calibration may not give the value di, especially since it is expressed in the measurement units of the detection cell 12, which are not necessarily used for calibration. Therefore, the value di is usually determined by the following relational expression: Lref ×CNRT(ti
)=di ×ti (21) That is, di = (Lref ×CNRT(ti)
)/ti (22) to the known value ti.

It will be recalled that Lref is the illumination that the film undergoes under certain known radiographic conditions when the film has reached a predetermined degree of darkening and non-reciprocal effects have been corrected. In order to finally determine the function CNRD and explain the final calibration of the method, it remains the method used to evaluate the reference illumination to be explained. This method is described in the above-mentioned METHOD FOR MEASUREMENT AND CALIBRATION OF ILLUMINATION EXPERIENCED ON X-RAY FILM.
THE ESTIMATION AND CALIB
RATION RECEIVED BY A RADI
OGRAPHIC FILM). The reference illumination varies depending on the optical density obtained on the film. In order to measure this illumination, as a first step, a sensitogram of the type of film used must be formed and photographed under defined X-ray exposure conditions and using a known thickness standard. Must be. These predetermined X-ray irradiation conditions are, for example, the following; a reference optical density DOref0 selected according to the user's normal usage, for example, DOref0=
1. Thickness standard E0, supply voltage V0, exposure time value t0
, the value of the product I0 ×t0 In this photographing, the optical density DO
m and the values M0, I0, t0 are measured. This allows the equivalent thickness Ep to be calculated using equation 7. Next, the radiation dose Df on the film is calculated using Equation 6. This gives the following formula; Lfil
m=Df ×I0 ×t0
(23) The illumination received by the film Lfilm
can be calculated. With reference optical density DOref0 it is possible to calculate the illumination step corresponding to the sensitivity curve of the film used (FIG. 5). This curve was drawn using a sensitometer and a densitometer. This allows consideration of the characteristics of the developing device used. The curve is, for example, recorded as a function in the microprocessor 19 (FIG. 1). Measured optical density DO
By m it is possible to calculate the measurement step Echm, which is the value of the irradiation step corresponding to DOm on the sensitivity curve (Fig. 5). The value of illumination on the film Lfil
m, reference stage Echref and measuring stage Echm to calculate the reference illumination Lref and determine the change in scale between the illumination and irradiation stages of the X-axis of the sensitivity curve (Fig. 5), i.e.: Formula; Echm = Echref + K log10 (Lf
ilm/Lref ) (24) can be used to obtain the optical density DOref0. The following formula is deduced from this formula 24; Lref = Lfilm x exp [log10]
(Echref-Echm)/K]] (
25) However, K=2/log102
(26) Photosensitivity constant K
corresponds to the scale selected in the irradiation stage. Value Lre
f via Lfilm according to equations 24 and 25,
determined by t0. Therefore, the value Lref is
Affected by the non-reciprocal action of the film. To correct for the non-reciprocity effect for the value Lref, in Equation 23,
The following formula; Lfilm=(Df ×I0 ×t0
)/CNRT(t0) (23'
) It is sufficient to use the value Lfilm determined by . This reference illumination Lref is the reference optical density D
Equation 25, which has to be used in Equation 10 to obtain Oref0, shows in particular that its illumination varies with the difference between the reference and measurement stages. Once the illumination experienced by the film is known, di is known by using Equation 22, and then CNRD(di) is calculated by Equation 20.

If the optical density of the X-ray film is not DOref0=1, repeat the above operation to obtain CNRT(
ti ) and Lref must be determined. To simplify these operations, perform the following steps to obtain the coefficients CNRT(ti); (g1)
When the exposure time is set to the reference time tref0, the first photosensitive gram Sref is determined by the variable time photosensitive graph.
0 and (g2) q photosensitograms S1 at different exposure times ti by variable time photographs.
~Sq (Fig. 5), (g3) select a reference optical density DOref0, for example, DOref0=1, and (
g4) For each sensitogram, the optical density DOref
Irradiation stages Echref0, Ech1 corresponding to 0=1
...Echi...Echq is measured, (g5) the following formula; CNRT(ti)=exp[log1
0 [(Echref0-Echi)/K]] (28
) calculate the coefficient CNRT(ti). If the user decides to operate with different optical densities, it is suggested to use optical densities intentionally corrected for the degree of darkening DOcvn, in order to avoid the above-mentioned calibrations. Next, the reference illumination Lref used in Equation 10 is replaced with the corrected illumination Lcvn. This corrected illumination Lcvn is expressed by the following formula; Lcvn = Lref ×exp [CVN/Γ×
P×log(10) ] (27) (However, in the above formula, −CVN is, for example, −10 to +
is an intentional correction of the degree of darkening indicated by an integer in the range of 10, where −P is a unit step of optical density, e.g.
0.1 and −Λ is the slope of the linear part of the sensitivity curve (FIG. 5).

[0021] In order to implement the above method, some calibrations are required. Their calibration is shown below; (
a) Analytical model using the following formula using a cartridge without a sensitivity plate; Dse=f' (Vm, Ep)
(4) Analytical model using the following formula using a cartridge and a sensitivity plate; Dc = f'' (Vm, Ep)
(6) Ep = g'' (Vm, Dc)
(7) Calibration of the X-ray equipment to determine. The amount of radiation absorbed by the sensitizing plate can be calculated from the difference Df = (Dse-Dc) (formula (8)). (b) Non-reciprocal CN displayed as a function of time.
Calibration of the film to determine the RT(t) law. This law is the non-reciprocal law CNRD expressed as a function of dose rate.
(d) is used to determine. (c) Calibration of reference illumination Lref. When performing each of these calibrations, the method of the invention consists of the following steps; (d)
The user selects a blackening value or an intentional correction value of the blackening degree to determine the target value of illumination Lcvn that the film should undergo under certain reference conditions, and determines the selected blackening degree (i.e. optical density). The target value illumination Lcvn is calculated by formula 27 (however, in this formula,
The illumination Lref is calculated using the calibration c and equations 25 and 26.
(determined by ). (e1)
Determination of the position of the object to be X-rayed (e2) Trigger of the start of exposure by the user (e3)
) Within the detection cell 12, the radiation dose D at time t'
Measurement of c1 (e4) Calculation of equivalent thickness E1 according to equation (7) (e5) Calculation of radiation dose Df1 in a film with thickness E1 according to equation (8) (e6) The following equation; Lf = Lam + Df1 × δmA ．． s
/CNRD (Film Dose Rate) Calculation of the illumination Lf received by the film by (9'), (e7
) The following formula; Lra=Lcvn −Lf
(1
0') selected degree of blackening (or optical density)
Calculation of the remaining illumination Lra required to obtain, (e8) the following formula; mAsra=(Lra/Df1)×C
NRD (Film Dose Rate) (11') Approximate m to obtain the selected degree of blackening (or optical density)
A. Calculation of mAsra to give s, (e9) work (e3) mA. emitted from the starting point. Measurement of s, (
e10) mA. measured in (e9). s is mA
When equal to or greater than sra, stop exposure, mA. measured in (e9). When s is less than mAsra, return to step (e3)

The above method description corresponds to a certain form of an X-ray device. When this device can take multiple forms, including selection about the size of the anode material focus, the presence or absence of a spectrally modified filter aiming anti-diffusion screen, the type of image receiver, the type of detection cell, for example: , respectively calibrate a for these forms,
It is necessary to carry out b and c. When a user implements the method of the invention, he determines a form, transfers the characteristics of this form to the microprocessor 19, and the microprocessor 19 uses the corresponding model. The method according to the invention applies to an image receiver 1 of the film/sensitizer combination type.
7 has been described, but it can also be implemented in the case of an image receiver 17 having only a film sensitive to X-ray radiation. For such films, the calibration of operations a and b is as follows; (
a') Calibrate the X-ray equipment and use the following analytical model; D'
f = f'''(Vm, Ep)
(30) Determine. However, film is used as the image receiver. In the method description below,
The following changes are made; step e3 includes detection cell 1
2, the radiation dose D'f1 after time t' is measured at e'3. Steps e4 and e5 are removed. Stages e6-e
8 is modified as follows. (e'6) The following formula; L'f = Lam + D'f1 x δmA. s/C
Calculation of the illumination L'f received by the film by NRD (film dose rate) (9''), (e'7)
The following formula; L'ra=Lcvn -L'f
(10'
') selected degree of blackening (or optical density)
The remaining lumination L'r required to obtain
Calculation of a, (e'8) The following formula; mAs'ra=(L'ra/D'f1)×CN
Calculation of mAs'ra, which is the remaining approximate mA.s emitted to obtain the selected degree of blackening (or optical density) by RD (film dose rate) (11''). Other steps e9 and subsequent The stage remains unchanged. It must be noted that in this case the sensitogram is of the In the case of a film/intensifier plate type image receiver, it is arranged behind the image receiver 17 or, if the irradiation energy allows this, in front of the image receiver 17.

Although the method according to the invention has been described for application to an X-ray apparatus (FIG. 1) in which the X-ray detection cell is located outside the image receiver, the method does not require that this detection cell 4 can also be applied to an X-ray device (FIG. 6) provided inside the image receiver 17. The image receiver 17 is then equipped with a film 3, an intensifying plate below this film 3, and its new detection cell below this intensifying plate 2. Such a new detection cell 4
“An X-ray Cassette with Automatic Exposure Detection Cell” filed on April 28, 1989
asset incorporating an
automatic exposure detect
French Patent Application No. 89 entitled ``R cell)''
This is the type described in No./05,668. This new detection cell detects and measures the light emitted by the intensifying plate 2 and is compared with the detection cell 12 that detects and measures the X-ray radiation behind the image receiver. As a result, there is no need to perform the first and second calibrations of the above method, thereby
It becomes possible to consider X-ray attenuation due to the film and the intensifying plate. Also, the corresponding stages e4 and e5 are:
There's no need. Thereby, the method follows the steps below (
(a) Calibration measures the reference illumination Lref that the film must undergo under certain reference conditions and determines the degree of darkening (or optical (b1) determine the position of the object to be irradiated with X-rays, (b2) the user triggers the start of exposure, (b3) measure the radiation dose Df1 after t' from the start of exposure, (b4) The following formula; Lf = Lam + Df1 x δmA. S
Calculate the illumination Lf received by the film by (9), and (b5)
The following formula; Lra=Lref −Lf
(10) Calculate the illumination Lra required to obtain the degree of blackening for a given optical density, and (b6) by the following formula; mAsr = Lra/Df1
(11) To obtain a predetermined degree of blackening (i.e. optical density), an approximate mA. mA giving s
sr and (b7) the mA.sr emitted from the beginning of step b3. s, and (b8) mA.s measured in step b7. s is mAs
When equal to or greater than r, the exposure is stopped and the mA. When s is less than mAsr, return to step b3. By using such a detection cell 4 inside the image receiver 17, the implementation of the method of the invention can be made easier. By this simpler method, which can be implemented when using the photodetection cell 4 inside the image receiver 17, steps a'', b1 to b8
It should be noted that, as far as this is concerned, all the features relating to the first aspect above can be utilized.

[Brief explanation of the drawing]

FIG. 1 shows a schematic block diagram of an X-ray apparatus with which the method according to the invention can be implemented.

FIG. 2 is a graph showing the curves obtained by implementing the calibration method used in the method according to the invention;

FIG. 3: Non-reciprocity coefficient CNRT as a function of exposure time t.
2 is a graph showing a curve representing a change in .

FIG. 4 is a graph showing a curve representing the variation of the non-reciprocity coefficient CNRT as a function of the reciprocal of the film dose rate d.

FIG. 5 is a graph showing a curve representing the change in optical density of an X-ray film as a function of illumination.

FIG. 6 is a schematic block diagram of an X-ray device similar to the X-ray device of FIG. 1, but in which the detection cell is built into the image receiver and receives the radiation emitted by the intensifying plate;

[Explanation of symbols]

11...X-ray source 12...detection cell 13...Object to be inspected 15...Power supply device 16... Integral circuit 17... Image receiver 18...Calculating device 19...Microprocessor

Claims (33)

[Claims] 1. An X-ray tube for emitting X-rays in the form of pulses of variable duration S toward an object to be examined, at least one intensifying plate and a film sensitive to the light emitted by the intensifying plate. an X-ray receiver for the X-rays passing through the object to be examined so as to form an image of the object; and a physical variable located behind the X-ray receiver and characterizing the X-ray beam. a cell for detecting the X-rays passing through the object to be inspected, capable of converting the signal into a measurement signal L; an integrating circuit that integrates the measurement signal L during an exposure time S and outputs a signal M; S and the anode current I of the X-ray tube
and a device for calculating the radiation dose D given as the ratio of M to the product I×S (or mA.s) of various values Vm for which the supply voltage V varies continuously or discontinuously.
A method for automatically determining the exposure time of an X-ray film in an X-ray apparatus for inspecting an object to be inspected, comprising the following steps: (a
) A first calibration of the radiographic apparatus is carried out with an object of thickness Ep using a receiver without one or more intensifying plates, with the following function; Dse=f' (Vm , Ep )
(4) and the following inverse function; Ep = g' (Vm, Dse)
(5) and (b) perform a second calibration of the X-ray imaging device with an object of thickness Ep using a receiver with an intensifying plate to obtain the following function; Dc = f'' (Vm, Ep)
(6) The following inverse function; Ep = g'' (Vm, Dc)
(7) and the following function; Df = f' (Vm, Ep) -
Determine f''(Vm, Ep) (8) and (c)
performing a third calibration that determines the reference illumination Lref that the film must undergo under certain reference conditions to achieve a degree of blackening (or optical density) selected as a reference value by the user; and the following steps: (e1) positioning of the object to be radiographed, (e2
) Trigger of initiation of exposure by user, (e3)
After the start of exposure, measurement of the radiation dose Dc1 at time t', (e4) calculation of the equivalent thickness E1 according to equation (7), (e5) radiation dose in a film of thickness E1 according to equation (8) Calculation of Df1, (e6) formula
Lf=Lam+Df1×δmA. s
Calculation of the illumination Lf received by the film according to (9), (e7) formula
Lra=Lref-Lf
(10) Calculation of the illumination Lra necessary to obtain the degree of blackening (or optical density) determined by (e8) Formula mAs
r=Lra/Df1
To obtain the blackening (or optical density) determined by (11), an approximate mA. Calculation of mAsr giving s, (e9) From the starting point of work (e3), mA. The measurement of mAsmes giving s, (
e10) mA. measured in (e9). When the measured value mAsmes of s is equal to or greater than mAsr, the exposure is stopped and the mA. A method characterized in that it comprises returning to step (e3) when s is smaller than mAsr. 2. The second calibration (b) above comprises measuring the equivalent thickness (sup.filter) by adding a filtering action between the intensifier plate and the detection cell and in equation 8 above. Ep (Ep -sup.filter)
The method according to claim 1, characterized in that it is carried out by substituting . 3. The step e10 is performed using the formula; tr = mAs
An operation involving calculating the remaining exposure time as r/I (e
'10), thereby making it possible to stop the exposure in open loop such that the exposure stops when the time tr has elapsed. 4. The step (e8) includes the steps e4 to e8.
During the period tc, the formula; mAsc = I×tc

(13) defined by mA. mA giving s
Calculate sc and use the formula; mAsra=mAsr − mAsc

(12), the mA. 3. Method according to claim 1 or 2, characterized in that the actual value mAsra of s is determined. 5. The step (e10) further comprises the formula;
trc=mAsra/I
(
14) Calculate the remaining exposure time trc shown by t
4. Method according to claim 3, characterized in that the exposure is stopped when rc becomes smaller than a value t0 corresponding to the interval between two successive steps (e3). 6. The above steps (e3) to (e10) are combined with the following operations: steps (e4) to (e8) and mA. s
CEtarget=mAsra×Dc
(
16) to convert the mA. A prediction task (T.
E. ) The target value CEtarge is determined by the signal received by the cell.
t is decremented, and the decremented value is the value Val.
4. The method according to claim 1, 2 or 3, characterized in that, when it becomes less than 0, it is replaced by a interrupting task (TC) consisting of terminating the exposure. 7. The prediction task (T.E.) is performed during exposure at moments t1 and t2 separated from each other for a period longer than a calculation time tc.
, . . . , tn. [Claim 8] Lf=Lam+Df1×δmA. s/CNR
D (film dose rate) (9') and mAsra=(Lra/Df1)×CNRD(
film dose rate) (11') (where, in these formulas, CNRD (film dose rate) is a non-reciprocal coefficient indexed as a function of the film dose rate at the receiver, and the film dose rate is: Df1×I

(1
7) Method according to any one of claims 1 to 7, characterized in that steps (e6) and (e8) are modified to take into account non-reciprocal effects represented by: 9. The coefficient CNRD (film dose rate) is
The following steps: Measure the non-reciprocity coefficient CNRT(ti) of the film/sensitizer pair as a function of the exposure time (ti), measure the film dose rate (di) for each exposure time (ti), and use the formula; CNRD(d)=A'0+A'1log(
1/d)+A'2[log(1/d)]2 (20) Calculate the standardization function of the coefficient CNRD(di), thereby calculating the coefficient corresponding to a given film dose rate. The method according to claim 8, characterized in that it is obtained by. 10. A method according to claim 9, characterized in that said film dose rate d is measured by said cell. 11. The film dose rate di is expressed by the formula;
di = [Lref ×CNRT(ti)]/
10. A method according to claim 9, characterized in that it is given by ti (22). 12. The non-reciprocal coefficient CNRT(ti), which is a function of the exposure time (ti), has the following steps: (a1
) change the X-ray tube heating current to obtain different values of this current; (a2) read the value M(ti) output by the integrating circuit for each different exposure time to obtain the optical density D01 of the film; , (a3) ratio
M(ti)/M(tref)
(29), whereby if ti = tref then the value M(
ti ) with M(tref )
12. The method according to claim 9 or 11, characterized in that it is obtained by calculating (ti). 13. The coefficient CNRT(ti) is calculated in the following steps: (g1) When the exposure time is set to the reference time tref0, the first photosensitive gram S is determined by a variable time photosensitive graph.
form ref0, (g2) different exposure times ti
Then, q sensitograms S1 to Sq are formed by a variable time sensitivity graph, and (g3) the reference optical density D
Select Oref0 and (g4) For each sensitogram, set the irradiation step Echr corresponding to the optical density DOref0.
Measure ef0, Ech1...Echi...Echq, and use the formula (g5); CNRT(ti)
=exp[log10[(Echref0-Echi)
12. The method according to claim 9 or 11, characterized in that it is obtained by calculating the coefficient CNRT(ti) by [/K]] (28). [Claim 14] Furthermore, a function; CNRT(t)=A0+A1 log
Claim 12, characterized in that it includes an operation of standardizing the coefficient CNRT(ti) in the form of an analytical model by t+A2 [log t]2 (18).
or the method described in 13. 15. Operation (c) of calibrating the reference illumination comprises the following steps; The image was taken under radiography conditions, the radiation dose D0 was measured, and the formula Ep0=g''(V0, D0)
Calculate the equivalent thickness Ep0 by (7) and use the formula Df0=f'(V0,E0)-f''(
V0, E0) Calculate the radiation dose Df0 on the film by (8) and use the formula Lfilm=Df
0×I0×t0
(23) calculate the brightness Lfilm on the film, calculate the illumination stage Echref corresponding to the reference optical density DOref0 by the sensitivity curve, measure the optical density DOm of the obtained photograph, and calculate the illumination stage Echm by the sensitivity curve. Calculate, formula; L
ref =Lfilm×exp [log10[(Ec
href −Echm )/K]] (25)
(However, K=2/log10(2)

15. A method according to any one of claims 1 to 14, characterized in that it comprises: calculating a reference illumination by (26) ). 16. The radiation dose Df on the film is expressed by equation 8.
To measure o, we convert the above equivalent thickness Epo to (Ep
o-sup. filter) to replace this sup. 16. A method according to claim 15, characterized in that filter is an additional filtering effect resulting from attenuation between the intensifier plate and the detection cell. 17. The brightness on the film is expressed by the formula;
Lfilm=(Df0×I0×t0)/CNRT(
17. The method according to claim 15 or 16, characterized in that it is calculated by t0 ) (23'). 18. The reference illumination Lref is
Formula; Lcvn = Lref ×exp [CVN/
Γ×P×log(10) ] (27)
(where, in the above formula, CVN is an intentional correction of the degree of darkening, e.g., indicated by an integer, P is the unit step of optical density, and Γ is the slope of the linear part of the sensitivity curve. 18. A method according to any one of claims 1 to 17, characterized in that it is replaced by a corrected illumination Lcvn such as ) to obtain different degrees of darkening (i.e. optical densities). 19. A method of applying the method according to claim 1 to an X-ray apparatus in which the receiver is of a film type and the detection cell is arranged in front or behind the receiver. and perform the above operations (a) and (
b) (a') Calibrate the above X-ray apparatus using film as an image receiver to form the following analytical model;
D'f = f''' (
Vm, Ep) (
30) Determine, and the above step (e3)
Step of measuring radiation dose D'f1 after time t'(e'3
), and steps (e4) and (e5) are removed,
The above steps (e6), (e7) and (e8) are (e'6
) Formula; L'f = Lam + D'
f1×δmA. s (film dose rate) (9''
) calculation of the illumination L'f experienced by the film, (e'7) formula; L'ra = Lcvn - L'f

The illumination L'ra required to obtain the selected degree of blackening (or optical density) by (10'')
Calculation, (e'8) formula; mAs
To obtain the selected degree of blackening (or optical density), the approximate mA. mAs' giving s
A method characterized by: calculating ra. 20. In the above equation (30), the above equivalent thickness Epo is replaced with (Epo-sup.filter), and this sup. 20. A method according to claim 19, characterized in that filter is an additional filtering effect resulting from attenuation between the intensifier plate and the detection cell. 21. An X-ray tube for emitting X-rays in the form of pulses of variable duration S towards an object to be examined, at least one intensifying plate and a film sensitive to the light emitted by the intensifying plate. an X-ray receiver for the X-rays passing through the object to be examined so as to form an image of the object; and a physical variable located behind the X-ray receiver and characterizing the X-ray beam. A cell for detecting the X-rays passing through the object to be inspected, capable of converting the measurement signal L into a measurement signal L, integrates the measurement signal L during the exposure time S, and converts the measurement signal L into a measurement signal L.
and a device for calculating the radiation dose D given as the ratio of M to the product I x S (or mA.s) of the exposure time S and the anode current I of the X-ray tube, and the supply voltage V various values Vm that vary continuously or discontinuously
X for inspecting the inspected object, which can take
A method for automatically determining the exposure time of an X-ray film in a radiographic apparatus, comprising the following steps:
a) Determine by calibration the reference illumination Lref that the film must undergo under certain reference conditions to obtain the degree of darkening (or optical density) selected by the user as the reference value, and then (b1) determining the position of the object to be exposed to X-rays; (b2) the user triggers the start of exposure; and (b3) t' from the start of the exposure.
Later, the radiation dose Df1 is measured, and the formula (b4) is obtained: Lf = Lam + Df1 x δmA
．． s (9)
Calculate the illumination Lf received by the film using the formula (b5); Lra=Lref −Lf
(
10) Calculate the illumination Lra necessary to obtain the degree of blackening (i.e. optical density) by (b6
) Formula; mAsr = Lra
/Df1
(11) to obtain the degree of blackening (i.e. optical density), the approximate mA. mAsr giving s
(b7) From the start of step b3, mA.
Measure the measured value mAsmes of s, (b8) ─
The mA. measured in step b7. When the measured value mAsmes of s is equal to or greater than mAsr, the exposure is stopped and mA.s measured in step b7. The measured value of s is mAsr
Returning to step b3 when smaller. 22. The step (b8) is performed using the formula; tr = mA
An operation comprising the step of calculating the remaining exposure time by sr /I (
22. Method according to claim 21, characterized in that, replacing e'8), the exposure can be stopped in open loop, whereby the exposure is stopped when the time tr has elapsed. 23. The step (b6) includes the steps b4 to b.
During the period tc of 6, the formula; mAsc = I × tc

(13) determined by mA. mA giving s
Calculate sc and use the formula; mAsra=mAsr×mAsc

(12), the mA. 22. The method according to claim 21, characterized in that the actual value mAsra of s is determined. 24. The step (b8) further comprises the formula;
trc=mAsra/I
(
14) Calculate the remaining exposure time trc shown by
23. Method according to claim 22, characterized in that the exposure is stopped when trc is less than a value t0 corresponding to the interval between two consecutive steps (b3). [Claim 25] The above steps (b3) to (b8) are performed as follows: steps (e4) to (e8) and CEtarge.
t=mAsra×Dc
(16) mA. mA to be given
．． Prediction task (T.E.) to predict s The target value CEtarget is decremented according to the signal received by the cell, and the decremented value becomes the value Val0 (V
22. The method according to claim 21, characterized in that when al0 becomes less than or equal to 0), a interrupting task (T.C.) consisting of terminating the exposure is substituted. 26. The prediction task (T.E.) is performed during exposure at moments t1 and t separated from each other for a period longer than a calculation time tc.
26. The method according to claim 25, characterized in that it is updated periodically with 2, . . . tn. [Claim 27] Lf=Lam+Df1×δmA. s/CNR
D (film dose rate) (9') and mAsra=(Lra/Df1)×CNRD(
film dose rate) (11') (where, in these formulas, CNRD (film dose rate) is a non-reciprocal coefficient indexed as a function of the film dose rate at the receiver, and the film dose rate is: Df1×I

(1
22. The method according to claim 21, characterized in that steps (b4) and (b6) are modified to take into account non-reciprocal effects represented by: 7). 28. The coefficient CNRD (film dose rate) is determined by the following steps: measuring the non-reciprocal coefficient CNRT(ti) of the film/sensitizer pair as a function of the exposure time (ti); di ), each exposure time (ti) is measured, and the formula; CNRD=A'0+A'1log(1
/d)+A'2[log(1/d)]2 (20) Calculate the standardization function of the coefficient CNRD(di), thereby calculating the coefficient corresponding to a given film dose rate. 28. A method according to claim 27, characterized in that it is obtained by carrying out. 29. The method of claim 28, wherein said film dose rate d is measured by said cell. 30. The film dose rate di is expressed by the formula;
di = [Lref ×CNRT(ti)]/
30. A method according to claim 29, characterized in that it is denoted by ti (22). 31. Operation (a) for calibrating the reference illumination comprises the steps of: predetermining the values of the reference optical density DOref0, the standard thickness E0, the supply voltage V0, the exposure time t0 and the product I0 ×t0. The radiation dose Dfo was measured using the formula Lfilm=Df0×I0×t0.
(
23), calculate the brightness Lfilm on the film, calculate the illumination stage Echref corresponding to the reference optical density DOref0 according to the sensitivity curve, measure the optical density DOm of the obtained photograph, and calculate the illumination stage Echref according to the sensitivity curve.
Calculate chm and use the formula; Lref = Lfilm×
exp [log10 [(Echref −Echm
)/K]] (25) (However, K=2/
log10(2)
30. The method of claim 29, comprising: calculating a reference illumination by (26) ). 32. The brightness Lfilm on the film is determined by the formula; Lfilm=(Df0×I0×t0)/
CNRT(t0) (23
32. The method according to claim 31, characterized in that the method is calculated by '). 33. The reference illumination Lref is
Formula; Lcvn = Lref ×exp [CVN/
Γ×P×log(10)]
(27) (where, in the above formula, CVN is an intentional correction of the degree of blackening, e.g. indicated by an integer, P is the unit step of optical density, and Γ is the linear part of the sensitivity curve. 33. A method according to claim 31 or 32, characterized in that it is replaced by a corrected illumination Lcvn, such as ?